UK accident investigators have attributed the fatal December 1999 crash of a Korean Air (KAL) Boeing 747-200 freighter to a faulty cockpit instrument and the crew's failure to respond to a developing emergency.

The captain's attitude director indicator (ADI) showed a correct pitch reading for the 747 during departure from London Stansted, but falsely showed the aircraft as being wings-level when it was actually in a dangerously steep left bank, says the UK Air Accidents Investigation Branch's (AAIB) report.

A fault in the ADI, correctly reported by a crew who had flown the aircraft to Stansted, was not rectified by the KAL ground engineer, who was among the four crew members killed in the accident. Investigators said the engineer failed to realise that the fault lay in the inertial navigation unit, which should have been replaced, and was instead misled by a separate but unrelated problem with avionics connections.

"Despite the accurate reporting of the fault in the technical log, supplemented by a verbal briefing, the aircraft departed Stansted carrying the same fault with which it had arrived," says the AAIB. It recommends that KAL either deploy sufficient engineers at its destination or delegate maintenance to a local service provider.

Investigators also highlighted the lack of communication between the crew members. Warning alerts and comments from the flight engineer on the ADI reading and the 747's attitude went unheeded, says the AAIB. It says that there is "no evidence to explain the commander's lack of response to a number of significant cues". But it adds that he may have trusted the instrument readings, while the inexperienced first officer - already previously criticised by the captain - could have been distracted or reluctant to speak up.